Integrated circuits are ubiquitous today. They are used for a very diverse set of consumer electronics, military electronics and commercial electronics. One concern that is becoming common to all devices that employ integrated circuits is the need to reduce the amount of power consumed. One way to reduce power consumption in a device is to turn off portions of the device that are not required at particular times (i.e., limit functionality, or remove power). In many cases, it is desirable to maintain power to other portions of the device in order to allow a user to quickly access the functions of the device.
FIG. 1 is a simplified block diagram of system 100. The system 100 can operate in either a “power on” mode or a “standby” mode. A peripheral input/output (I/O) power supply 101 supplies power to one or more I/O devices 103. This power is always provided. The I/O devices 103 may include such things as an infra-red detector for receiving inputs from a infra-red emitting remote control device, such as a television or set top box remote control. Other such I/O devices include: (1) receivers for Multimedia over Coax Alliance (MoCA) commands received over an interface that operates in accordance with the well-known MoCA standard for communications over coaxial cable; (2) front panel controls; (3) Ethernet receivers; (4) radio frequency (RF) receivers; or (5) local area network (LAN) receivers. By ensuring that power is always supplied to the I/O devices, such I/O devices remain functional and thus allow commands to be received to move the system 100 from standby mode to power on mode.
A relatively larger external main power supply 102 is connected to a standby island 104 within an integrated circuit 106. The external power supply is also connected to a switch 108 that allows power to be connected to a core 110 of the integrated circuit 106 when in the system 100 is in power on mode or, alternatively, to the standby island 104 within the integrated circuit 106 during standby mode. The core 110 essentially includes all of the circuitry of the integrated circuit 106 that is not within the standby island 104. The core power requirement is much greater than that of the standby island 104. In some instances, the core 110 may draw as much as 4 Amps. However, the core 110 can be powered down during standby mode. Therefore, the switch 108 has to be capable of handling relatively high current with a minimal voltage drop. This requires the switch 108 to have a very low “on-resistance”. Such switches are difficult to integrate into the integrated circuit 106. The result is that the system cost is increased due to the expense of the external switch (typically a large field effect transistor).
Accordingly, there is presently a need for a low cost means for switching from power mode to standby mode.